The present invention relates to a variable shaped electron beam exposure system, and a method of writing a pattern on a resist with a variable shaped electron beam exposure as well as a storage medium having stored a computer program for execution of a variable shaped electron beam exposure to write any patterns on the resist, and more particularly to a variable shaped electron beam exposure system suitable for forming application specific integrated circuits (ASICs) with less regularly repeated patterns or for logic devices of microcomputers, and a method of writing a pattern on a resist with a variable shaped electron beam exposure for forming the same as well as a storage medium having stored a computer program for execution of a variable shaped electron beam exposure to write any patterns on the resist.
The electron beam exposure methods are classified into two typical types. The first one is one-shot electron beam exposure in projection mode using a mask. The second one is a variable shaped electron beam exposure without use of any mask.
The one-shot electron beam exposure systems operable in projection mode using the mask are disclosed in Japanese laid-open patent publications Nos. 6-140305 and 7-56318. An electron beam is emitted from an electron gun for projecting a pattern image of a mask through a projection system onto a resist over a wafer. This method is suitable for writing regularly repeated patterns on the resist over the wafer, for example, in order to form dynamic random access memory devices and static random access memory devices.
In the meantime, the variable shaped electron beam exposure method is suitable for random patterns with less regularly repeated patterns, for example, in order to form the application specific integrated circuits (ASIC) and the logic devices of the microcomputer.
FIG. 1A is a view illustrative of first and second aperture plates with first and second apertures used in a conventional variable shaped electron beam exposure system. The conventional variable shaped electron beam exposure system has a first aperture plate 31 with a first aperture 30 which is rectangular-shaped and a second aperture plate 33 with a second aperture 32 which is also rectangular-shaped, so that the electron beam emitted from the electron gun is firstly defined by the first aperture 30 and then deflected by a deflector not illustrated for subsequent second definition of the electron beam by the second aperture 33. The electron beam shaped by the first and second apertures 30 and 32 are transmitted to the resist over the wafer. By controlling or adjusting the deflection of the electron beam by the deflector, the shape of the electron beam having penetrated through the first and second apertures 30 and 32 are varied.
FIG. 1B is a plane view illustrative of first and second apertures of the conventional variable shaped electron beam exposure system. The first and second aperture plates 31 and 33 are placed to have a distance in a direction along which the electron beam is transmitted. The first and second aperture plates 31 and 33 are also placed to be relatively displaced from each other on a plane vertical to the direction along which the electron beam is transmitted, so that, in the plane view, the fist and second apertures 30 and 32 are partially overlapped to have a rectangular-shaped overlap area 34 through which the electron beam is transmitted. Namely, the electron beam having penetrated through both the first and second apertures 30 and 32 are defined to have the same shape as the rectangular-shaped overlap area 34. As a result, the resist over the wafer is exposed to the rectangular-shaped electron beam having been shaped by the first and second apertures 30 and 32.
FIG. 1C is a plane view illustrative of completely overlapping first and second apertures of the conventional variable shaped electron beam exposure system. The first and second apertures completely overlap to have a maximum overlap area 35 with the same shape as the first and second apertures 30 and 32. The maximum overlap area 35 may be considered to be a maximum electron beam exposure area which means the maximum area of a single time variable shaped electron beam exposure. This means it necessary to divide each of the required patterns with optional shapes into plural rectangular-shaped unit patterns which are, however, smaller in size than the maximum electron beam exposure area so that the variable shaped electron beam exposures are sequentially conducted to sequentially write the divided rectangular shaped unit patterns. FIG. 2 is a plane view illustrative of one of required patterns, each of which is divided into unit patterns by separation lines 36. Six required patterns with different shapes are individually divided by the separation lines 36 into thirty three rectangular-shaped unit patterns which are smaller in size than the maximum electron beam exposure area. The electron beam is variably shaped by adjusting the overlapping area of the first and second apertures 30 and 32 so that the electron beam has the same shape as the rectangular shaped unit pattern.
In recent years, it has been required to shorten the necessary time for the electron beam lithography process as the variation of the logic devices has been increased and the production in a small scale has been required.
However, the required patterns with different shapes are individually divided into many rectangular-shaped unit patterns which are smaller in size than the maximum electron beam exposure area for sequential exposures for every the rectangular-shaped unit patterns. This means it difficult to shorten the necessary time for the electron beam lithography process, resulting in a drop of the throughput.
If further the required pattern has a complicated shape, then such the pattern is divided into may fine rectangular shaped unit patterns. This may raise an issue of increased variation in size of the required pattern, whereby the accuracy in writing the pattern is dropped.
In the above circumstances, it had been required to develop a novel variable shaped electron beam exposure system and a method of writing a pattern on a resist with a variable shaped electron beam exposure free from the above problems and disadvantages, as well as a storage medium having stored a computer program for execution of a variable shaped electron beam exposure to write any patterns on the resist.